Field of the Invention
This invention relates to vacuum operable differential servo-motor used to operate, for example, the known hydraulic brake system, anti-skid brake control systems and the like for use on motor vehicles.
Description of the Prior Art
Differential servo-motors as they are known conventionally in the art, usually include a housing having a movable wall structure or piston positioned therein for reciprocable movement in the housing, the movable wall structure dividing the housing into two compartments, one on each side of the movable wall. The compartments are usually in fluid communication with an engine intake manifold for obtaining the vacuum pressure from the engine intake manifold.
In order to sense any failure of the movable wall for safety purposes, an electric switching member is employed in the prior art in engagement with the movable wall.
There exists however a tendency of ingress of evaporated fuel from the engine intake manifold into the compartments and hence into the switch member, since the switch member is outside of the housing and the operative connection is achieved across a wall portion of the housing with the movable wall in the housing. This tends to cause a danger of explosion of the fuel vapor due to a spark of the electric switch member.
In order to avoid such danger, many switch members have employed complicated sealing mechanisms to isolate the interior of the switch members from the compartments of the housing. This attained the safety purpose successfully but undesirably for decreasing the substantial manufacturing costs.